1. Field of the Invention
The present invention relates to a working/standby clock pulse supply for digital systems with an operating clock oscillator which supplies an operating clock signal and with a standby oscillator which supplies a standby clock signal and with at least one assembly to which the working clock signal and the standby clock signal are supplied.
2. Description of the Prior Art
In digital data processing systems, multiplex systems, switching systems and, particularly, cross-connect multiplex systems in synchronous networks, generally a standby clock pulse supply is provided. In larger systems, several equipment packs operate in synchronous fashion with a clock pulse, whereby it is possible to process data signals in parallel. In order to achieve a higher operational dependability, two or more central clock signals that are coupled with each other are offered to all units. The central clock signals are provided by crystal oscillators (VCO's) which, for their part, are synchronized to a highly-accurate standard clock signal. If the standard frequency fails, the frequency accuracy of the crystal oscillators is sufficiently high at first to guarantee a further operation of the system. If the operating clock pulse oscillator fails, if it is being repaired or in the case of an interruption of the clock signal path, it has so far been usual to switch over to standby clock signals. Hereby, usually-heavy disturbances occur during the transition from the operating clock signal to the standby clock signal which could lead to a higher loss of bits and therefore also to a loss of synchronism. Since all assemblies must be provided with the same clock pulse failure circuit, a simple and inexpensive solution is necessary.